Selective staining of rodent acrosomes with phosphotungstic acid

The acrosome of rodents, as well as the acrosomal granule,the head cap and the elastic materials fixed in glutaraldehyde and embedded in EPON, show a high degree of affinity for aqueous phosphotungstic acid (PTA). Under the electron microscope the reactive material shows up in strong contrast when fine sections have been floated on aequous 3-5 % PTA. In thick PTA-treated sections, the PTA can be easily located by light microscopy by subsequent staining with methyl green pyronin or UNNA's blue.